Hackernoon how to implement trie (prefix tree) – blind 75 leetcode questions

Hackernoon how to implement trie (prefix tree) – blind 75 leetcode questions

In the competitive realm of coding interviews, mastering the Blind 75 LeetCode questions is a monumental task that demands strategic preparation and a deep understanding of fundamental data structures and algorithms. Among these, the Trie, also known as a prefix tree, stands as a crucial tool for efficiently solving a variety of problems. In this comprehensive guide, we’ll delve into the intricacies of Trie implementation and explore how it can be wielded effectively to conquer the Blind 75 challenges on LeetCode.

Understanding the Significance of Trie

What is a Trie?

A Trie is a tree-like data structure that is particularly adept at storing and retrieving strings in a manner that allows for efficient prefix-based operations. Unlike traditional data structures such as arrays or hash tables, which store data sequentially or based on hashed values, a Trie organizes strings in a hierarchical fashion based on their common prefixes.

Why Trie Matters in Coding Interviews

In the context of coding interviews, where efficiency and optimization are paramount, the Trie offers several advantages. Its ability to swiftly search for words with a common prefix makes it invaluable for tasks such as autocomplete, spell-checking, and word validation. Moreover, Trie’s space-efficient nature and quick lookup times make it an ideal choice for scenarios involving large dictionaries or sets of strings.

Step-by-Step Guide to Trie Implementation

Step 1: Define the TrieNode Class

The foundation of any Trie implementation lies in the TrieNode class, which represents each node in the Trie. Each TrieNode typically contains a reference to its child nodes, along with additional metadata such as whether the node marks the end of a word.

Step 2: Initialize the Trie

Once the TrieNode class is defined, the next step is to create the Trie class itself. This class serves as the entry point for Trie operations and typically contains methods for inserting, searching, and deleting words from the Trie.

Step 3: Implement Trie Insertion

Inserting a word into the Trie involves traversing the Trie from the root node, creating new nodes as necessary to represent each character of the word. At the end of the insertion process, the final node representing the last character of the word is marked as a terminal node to indicate the presence of a complete word.

Step 4: Implement Trie Search

Searching for a word in the Trie follows a similar process to insertion, with the key difference being that we’re not creating new nodes. Instead, we traverse the Trie based on the characters of the target word and check if each character exists in the Trie. Additionally, we verify whether the final node representing the last character is marked as a terminal node, indicating a complete word.

Step 5: Trie Deletion (Optional)

While not always necessary for solving LeetCode problems, implementing trie deletion involves removing a word from the Trie by recursively removing its corresponding nodes. This process can be complex due to considerations such as handling nodes with multiple children and ensuring the integrity of the Trie structure.

Applying Trie to Blind 75 LeetCode Questions

With a solid understanding of Trie implementation in hand, let’s explore how this data structure can be applied to solve some of the Blind 75 LeetCode questions.

Example 1: Word Search II

In the Word Search II problem, we are tasked with finding all words from a given list that can be formed by traversing adjacent cells on a 2D board of characters. By first constructing a Trie containing all the words in the list, we can efficiently search for each word in the Trie while performing a depth-first search (DFS) on the board. This approach drastically reduces the time complexity compared to brute-force methods, allowing us to solve the problem within the given constraints.

Example 2: Implement Trie (Prefix Tree)

The Implement Trie (Prefix Tree) problem itself is an excellent exercise for mastering Trie implementation. By following the step-by-step process outlined earlier, we can create a Trie class capable of inserting, searching, and prefix searching words efficiently. This foundational knowledge lays the groundwork for tackling more complex problems that leverage the Trie data structure.

Tips for Success

Practice Regularly

As with any skill, mastery of Trie implementation and its application to coding problems requires consistent practice. Dedicate time to solving Trie-related problems on platforms like LeetCode, HackerRank, or CodeSignal to reinforce your understanding and identify areas for improvement.

Understand Problem Constraints

Before diving into solving a problem, take the time to thoroughly understand the constraints and requirements outlined in the problem statement. Pay attention to edge cases and special scenarios that may influence your approach to implementing Trie or solving the problem overall.

Optimize for Efficiency

Efficiency is key in coding interviews, so strive to optimize your Trie implementations and algorithms for both time and space complexity. Experiment with different approaches, data structures, and algorithms to find the most efficient solution for each problem.


Mastering Blind 75 LeetCode questions requires not only proficiency in problem-solving techniques but also a deep understanding of essential data structures like the Trie. By following this step-by-step guide to Trie implementation and applying it to relevant coding problems, you can enhance your problem-solving skills and increase your chances of success in coding interviews and competitive programming competitions. Start practicing today and embark on your journey to Trie mastery!

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